The surface of human skin is composed of corneocytes, which are degenerated keratinocytes that have differentiated and grown from the basal layer. The corneocytes are bound by ceramide lamellar structures abundant in the stratum corneum and maintain the skin smooth and elastic.
Since ceramides are hardly soluble, they are prepared into small-sized particles when used in cosmetic products in large quantities. In this case, stability may decrease and gelation may occur. If the particle size is small, interparticle attraction increases greatly due to increased surface energy between particles. As a result, the ceramide particles tend to aggregate with each other, not being perfectly dispersed in an oil phase but being released into an aqueous phase. Gelation occurs as a result of the binding between the ceramide particles.
To solve this problem, granules prepared from ceramides, stearic acid, cholesterol, etc. are added at the last step of emulsion preparation to induce stabilization of ceramides. That is to say, by dispersing ceramides in an emulsion after stabilizing them by preparing into solid granules, the fluidity of the ceramides is removed and stability is improved. Korean Patent Application No. 2008-0072355 discloses ceramide granules including a shell solidified using a nucleation agent.
However, this method is problematic in that the amount of ceramides that can be used in a composition for skin external use is decreased because a large quantity of encapsulation agent has to be used for encapsulation of ceramides. In addition, use of the sugar- or polymer-based encapsulation agent impairs usability which is essential for the composition for skin external use.